JS300/650 Build
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Thread: JS300/650 Build

  1. #1
    PWCToday Newbie Warrior1996's Avatar
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    JS300/650 Build

    Hi guys, new to the stand up jet ski world. Recently I bought a JS300 that had all the guts from a JS550 in it (550 engine, pump...). PO sold it to me for cheap because the day before he lost compression in the rear cylinder while out for a ride. I was originally planning to rebuild it but after finding a bad crank, decided to swap engines instead. I found a clean TS650 for a good price so I went and took a look at it. The engine had 135/130 psi on a cold engine with the throttle closed (fail on my part during the compression check), so I bought it.

    Plan for the build is pretty simple, and I've done a fair bit of research on this forum, but decided I'd like everyone's opinion on a few things prior to me starting the build.

    Cooling: The JS300 hull is already setup for dual cool (using the stock cooling line and the bilge line), but the line size is too small for a 650 imo. (Looking at about 1/4" ID). My current plan is to run dual cooling, with one 1/2" line and one 3/8" line. I'm thinking I will use the 1/2" line to cool the engine and use the 3/8" line to cool the exhaust/waterbox. This seems overkill but I want to be safe in the future because knowing myself, I will continue to mod the engine for more power once I learn how to ride this thing... I was thinking I could use some flow control valves to control the water if it is too much cooling for the stock-ish 650 that'll be in there. Opinions Please!!!!

    Impeller: The JS550 pump currently has a 16 pitch Skat Trak impeller. I've been reading that people typically use anywhere from 17 to 19 pitch impellers. I'm currently thinking an 18 pitch would be about right, but opinions are welcome.

    Engine Mods: I plan to deck the head to up the compression. I've read 0.020" will get me closer to 180 psi. I want to run 93 octane, so I definitely don't want more than 180 psi. For starting, I'm going to run the stock carb. This will likely be swapped for a sbn44 or 46 sooner than later.

    Exhaust: I have a stock 650sx exhaust system for this project that I will be doing the "dry pipe" mod to. I'm going to use a Mariner JS550 waterbox.

    JS300 Current Mods: Quick steer, straight bars, electric bilge pump, Mariner extended ride plate, Team Butch intake grate, skat trak impeller

    Mods to come along with 650 swap: extended gas tank, new turf, hull braces, pump stuffer (maybe), lock-on grips.

    Goal is to make it almost a sleeper, keeping the stock original graphics, etc. Thanks for any input you guys can give.

    20180710_200039.jpg20180710_200151.jpg20180904_183755.jpg

  2. #2
    PWCToday Newbie
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    Re: JS300/650 Build

    Suzuki 639cc. (Tigershark 650 engine) single carb, 62hp.
    I type that having run a Kawi550/Kawi 650. Wasn't too awesome.
    I'd try to swap the kawi for suzook. yes I would. Far easier task. imho.

  3. #3
    PWCToday Newbie Warrior1996's Avatar
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    Re: JS300/650 Build

    Well I have the 650 and the exhaust needed already, so definitely sticking with the Kawasaki. I've also heard a lot of bad things about the Tigersharks, so not sure why I'd want one...

  4. #4
    PWCToday.com Is My Home Away From Home Rushford_Ripper's Avatar
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    Re: JS300/650 Build

    I used a 15/20 pitch impeller in mine, really liked the results. Impros can repitch your impeller if you go that route. Sbn44 is a good choice but donít rule out a keihin 38 as they perform well. I would stick to a single cooling setup it it was me, cools it just fine or just use what you have for dual stock, donít think you need to increase the size from 3/8 line.
    Last edited by Rushford_Ripper; 10-02-2018 at 07:26 PM.


  5. #5
    PWCToday Newbie Warrior1996's Avatar
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    Re: JS300/650 Build

    Quote Originally Posted by Rushford_Ripper View Post
    I used a 15/20 pitch impeller in mine, really liked the results. Impros can repitch your impeller if you go that route. Sbn44 is a good choice but don’t rule out a keihin 38 as they perform well. I would stick to a single cooling setup it it was me, cools it just fine or just use what you have for dual stock, don’t think you need to increase the size from 3/8 line.
    Did you run a single 1/2" line? The TS650 hull has a single 1/2" line through the hull, but the entire engine uses 3/8 line. I imagine the 650 pump only has a 1/8" NPT fitting in it stock, but I haven't measured...

  6. #6
    PWCToday.com Is My Home Away From Home Rushford_Ripper's Avatar
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    Re: JS300/650 Build

    I used the 550sx pump and cooling in stock form


  7. #7
    PWCToday Newbie Warrior1996's Avatar
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    Re: JS300/650 Build

    Quote Originally Posted by Rushford_Ripper View Post
    I used the 550sx pump and cooling in stock form
    Ok, well then the dual cool with 3/8" line should be good enough then. That'll save me some work

  8. #8
    PWCToday Newbie Warrior1996's Avatar
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    Re: JS300/650 Build

    Does anyone else have an opinion on impeller size? Want to get one ordered but now I'm not sure if I should go with a 15-20 variable pitch or an 18 or 19 straight pitch.

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